Complementary metal-oxide semiconductor (CMOS) image sensors are gaining in popularity over traditional charged-coupled devices (CCDs) due to certain advantages inherent in the CMOS image sensors. In particular, CMOS image sensors typically require lower voltages, consume less power, enable random access to image data, may be fabricated with compatible CMOS processes, and enable integrated single-chip cameras.
Generally, CMOS image sensors utilize light-sensitive CMOS circuitry to convert light energy into electrical energy. The light-sensitive CMOS circuitry typically comprises a photo-diode formed in a silicon substrate. As the photo-diode is exposed to light, an electrical charge is induced in the photo-diode. The photo-diode is typically coupled to a MOS switching transistor, which is used to sample the charge of the photo-diode. Colors may be determined by placing filters over the light-sensitive CMOS circuitry.
A CMOS image sensor typically comprises an array of CMOS image pixels, each of which may include transistors (switching transistor and reset transistor), capacitors, and a photo-sensitive element (e.g., a photo-diode). Each pixel may also include a color filter to determine a color of light received by the photo-sensitive element. An aperture is generally formed over the photo-sensitive element to expose the photo-sensitive element while blocking the light from the other circuitry.
The performance, sensitivity, and resolution of the CMOS image sensors, however, may be degraded due to crosstalk caused by light being received at oblique angles to the aperture generating an electrical current in other parts of the circuitry. As a result, the magnitude of the light being received may be falsely magnified, possibly resulting in a “washed out” or blurred image. Additionally, light being received at oblique angles to the aperture may also generate a current in adjacent pixels. In the case in which color filters are being used, the current being received by an adjacent pixel may have the detrimental effect of falsely indicating the colors being received by each pixel.
Accordingly, there is a need for an image sensor having a light shield that prevents or reduces crosstalk.